Electric fuel pump questions. - page 2 - Upgrades (non engine related ) - VWDiesel.net The IDI, TDI, and mTDI source.
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#15 by theman53 on 10 Aug, 2011 15:50
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I guess.
I just seem to find if I leak diesel on a rad hose it soaks into it and it turns into a trojan. I don't mess with enough gas powered anymore to remember what it does when that happens. It probably evaporates too fast to mess with it.
I did email some MFG and asked if the regulators would work with diesel and they all said, "no" and that was it. No reason just no. -
#16 by R.O.R-2.0 on 11 Aug, 2011 09:36
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I guess.
I just seem to find if I leak diesel on a rad hose it soaks into it and it turns into a trojan. I don't mess with enough gas powered anymore to remember what it does when that happens. It probably evaporates too fast to mess with it.
I did email some MFG and asked if the regulators would work with diesel and they all said, "no" and that was it. No reason just no.
they probably thought you were a retard, and wanted to use it on a common rail engine or something like that..
there are some BRILLIANT people out there, with some BRILLIANT epic fails.. lol. -
#17 by burn_your_money on 14 Aug, 2011 08:22
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Using the above image for reference, at idle and probably throughout the entire RPM range (possibly not for heavily modified pumps) the feed pump is flowing more fuel than is needed by the engine. This, added to the fact that there is a restriction in the OUTLET banjo bolt creates pressure inside the pump housing. This pressure is the main thing that controls advance. On some pumps it is the only thing. Pressure is regulated by the regulating valve.
The feed pump is a positive displacement pump. What that means is that whatever goes into must come out. Our waterpumps are an example of a non-positive displacement pump (I think that is the term). It basically just spins and will push some of the coolant around. Back to the feed pump. What this means is that flow is related to RPM in a linear fashion. The higher the RPM, the more fuel will be pushed into the pump housing.
At idle, the regulating valve will be partially open. Any fuel that the regulating valve bleeds off to maintain the proper PSI in the pump housing is directed back to the feed side of the feed pump. See below
That "extra" fuel is supplementing the amount of fuel that needs to be drawn from the tank. When you mash the go pedal, the balance is upset. More fuel is injected into the engine but the engine and pump RPM has not increased yet. This causes the pressure inside the pump housing to begin to drop. As the pressure begins to drop, the regulating valve begins to close and direct more fuel into the pump housing rather than back into the feed side of the feed pump. The regulating valve is very sensitive so the pressure drop is minimal on our engines.
Yes, the feed pump on the cummins and the VW is the same. When we look at the two engines, the VW has 4800 RPM to make it's power while the cummins has 3000. Going back to the positive displacement feed pump we can see that the VW has an advantage in maintaining internal pump pressure throughout the RPM range. Also consider the fact that a cummins idles around 600 RPM while our VWs are around 800 RPM. That's 30% more flow through the vane pump at idle on our VWs.
Also, on many VE pumps, when you mash the go pedal at idle the amount of fuel injected into the engine is the maximum amount of fuel that will ever be injected into the engine. The exception is starting fuel, or cranking fuel. Bosch has developed many fancy contraptions to modify the fuel curve that make my above statement false, such as the LDA but the point I am trying to make is at idle and WOT a lot of fuel is being injected into the engine.
The above statements are based on a properly calibrated pump. Over the years parts wear and the pump falls out of calibration. Depending on the wear of your pump you may find that a lift pump helps. Like ROR said, it is especially helpful in priming the fuel system for starting. -
#18 by dl_sledding on 21 Aug, 2011 15:10
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besides, doesnt gas come from higher up on the evap tower at the refinery?
that means they refine diesel even more to get gas from it..
Nope, got that backwards... From http://www.emt-india.net/process/petrochemical/Petroleum.htm: "Crude oil is refined into products such as gasoline, asphalt, and waxes by a process called fractional distillation. During the process, the parts, or fractions, of crude oil are divided out successively by their increasing molecular weight. For instance, gasoline has a low molecular weight and vaporizes at a fairly low temperature. This means that at the appropriate temperature, while all of the rest of the oil is still in liquid form, gasoline may be separated out. The remaining oil goes through the same process at a slightly higher temperature, and jet fuel is divided out. Repeating the distillation process several times will separate out several constituents of crude oil, which are then processed and put to a wide range of uses."
Gas is the first (and most abundant) product in crude oil. More than half of each barrel is gasoline, the rest is everything from kerosene to tar. There's only like 3 gallons of diesel in each barrel, so gas is 7 times more abundant than diesel.
I suppose that kind of explains why gasoline is more corrosive... Because it is really kind of the "base" of the crude, and will be able to mix with anything below it in the stack? Whereas diesel is much closer to the rubber products, and less likely to dissolve the rubber? Assuming, of course, it's synthetic rubber (made from petroleum and not from natural latex).
The last paragraph is all conjecture. I hate chemistry. Never was able to understand that magic. -
#19 by monomer on 23 Aug, 2011 16:38
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A lot of diesel sold around here has a small percentage of Biodiesel added (B5)
This would explain the swelling on rubber -
#20 by dodger21 on 23 Aug, 2011 19:24
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Well, personal experience talking here.
On the VE'd Cummins, the stock diaphragm pump only puts out 5psi max. 3 or so at idle. And only when new. Some people with stock systems and new lift pumps (The old non-intercooled ones. They have a bigger injector) can pull their pressure to 0.
There is a rumor that anything above 16-20psi will blow out the front seal. However, these are on old 20 year old pumps with +200k miles.
I personally ran a Walbro 392 (Max PSI 140, Max flow 85GPH) regulated at 18psi. More power (dropped .2 sec in the 1/4mile), better mileage(+1-2mpgs), less smoke throughout the RPM range but noticed the most @ WOT.
Personal friends run Procomp Black that come regulated at 14psi and the hold up just fine.
If you run the Holley or Procomp black, mount as close to the tank and at bottom or below the tank. They are meant to "push" rather than "pull" the fuel.
If you run greater than 10psi, it does affect the timing piston. IIRC, anything above 13 or 14psi give it full forward advance. -
#21 by burn_your_money on 24 Aug, 2011 10:27
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If you run greater than 10psi, it does affect the timing piston. IIRC, anything above 13 or 14psi give it full forward advance.
Not on a VW pump, and I would be very surprised if the Cummins pumps were different. If you look at the first picture I posted it shows that the added pressure will equally effect both sides of the advance piston, thereby nullifying any effect on timing. I have personally tested this on a test bench with Giles. I forget how high in PSI we went, but it was over 40PSI and the timing gauge did not move. -
#22 by Toby on 05 Nov, 2011 23:22
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besides, doesn't gas come from higher up on the evap tower at the refinery?
Gas is the first (and most abundant) product in crude oil. More than half of each barrel is gasoline, the rest is everything from kerosene to tar. There's only like 3 gallons of diesel in each barrel, so gas is 7 times more abundant than diesel.
Actually if you read the article you quoted a "barrel of crude" (whatever that may be) is only about 25% gasoline. Much more is made by thermal and catalytic "cracking" of the heavier fractions.
The rub here is that "crude oil" is vastly different depending where it is pumped. Venezuelan crude is said to be "heavy" because it is low in lighter fractions like naptha and gasoline and high in oils and tars. Indonesian crude is so "light" that it can be bunkered (burned) in ships w/o being refined. That is why the Japs went into Indonesia very early in WWII. They pumped the crude directly into the Imperial Japanese naval vessels. -
#23 by Toby on 05 Nov, 2011 23:27
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So has anyone yet tried adding a lift pump? I may add a lift pump to my recently acquired Volvo D24 wagon. The vanes appear to be stuck in the feed pump and all it will do is idle. It has an outboard primer bulb between filter and pump and giving it a squeeze will allow the engine to rev up. I am putting off disassembling the pump until I get a clean bench.
That won't answer the question however, but at least I should be able to drive the car. -
#24 by Patrick on 06 Nov, 2011 02:57
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I'm running the gas pump in the tank on my mk2 jetta all the time, feeding an AAZ... Did it that way in March this year when I moved the AAZ from the last car it wore out. Haven't had any problems.
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#25 by R.O.R-2.0 on 06 Nov, 2011 08:45
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So has anyone yet tried adding a lift pump? I may add a lift pump to my recently acquired Volvo D24 wagon. The vanes appear to be stuck in the feed pump and all it will do is idle. It has an outboard primer bulb between filter and pump and giving it a squeeze will allow the engine to rev up. I am putting off disassembling the pump until I get a clean bench.
That won't answer the question however, but at least I should be able to drive the car.
i got a lift pump, it rocks.
really shines on the top end where the pump would be pulling the most vacuum..
got more power from it, and it seems like better mileage. -
#26 by Toby on 06 Nov, 2011 09:02
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I thought you had a worn out IP though. I was curious about the performance of a lift pump on an otherwise good IP. What is the issue with your IP, BTW.
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#27 by R.O.R-2.0 on 06 Nov, 2011 09:51
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I thought you had a worn out IP though. I was curious about the performance of a lift pump on an otherwise good IP. What is the issue with your IP, BTW.
contrary..
my IP was rebuilt less than 15k miles ago. got the paperwork.
it helped out a worn out IP a little bit.
it helped out a brand new IP ALOT!
my issue is that i added a little 2 micron after-filter ahead of the stock filter, and it made the filter work harder to pull fuel thru 2 filters., so i added the lift/primer pump..
holy crap, what a difference it made. the pick up off the bottom end is night and day different. its got considerably more bottom end power, and alot more top end power.. -
#28 by Toby on 06 Nov, 2011 10:17
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Maybe I will try adding a lift pump to the 5G while I still have it, and see if there is a difference then..
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#29 by R.O.R-2.0 on 06 Nov, 2011 10:23
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its worth a try.
i never even considered it until i had my 2 filters. then i was pleased with the results.
all i used was a cheapo shaker style fuel pump.